High mobility and excellent thermoelectric performance monolayer ZnX₂Z₄ (X = In, Al, Ga; Z = S, Se, Te) materials

Recently, two-dimensional (2D) layered polarized ZnIn₂S₄ nanosheets have been successfully synthesized in experiments. However, the polarized monolayers are unstable in air, which hinders their practical applications. Therefore, in this work, we proposed a new family of nonpolarized monolayers (β₂-phase) ZnX₂Z₄ (X = In, Al, and Ga; Z = S, Se, and Te) by first-principles. It is confirmed that the energies of β₂-phase ZnX₂Z₄ are lower than those of the polarized and β-phase ZnX₂Z₄ monolayers. Moreover, these ZnX₂Z₄ monolayers have not only desirable indirect band gaps but also high electron mobility (up to 10³ cm² V^-1 s^-1), revealing a fascinating visible light absorption range. Furthermore, β₂-phase ZnX₂Te₄ (X = In, Al, and Ga) has ultra-low lattice thermal conductivity and high ZT value (up to 0.89), suggesting that these monolayers can be good candidates for thermoelectric materials. These new 2D ternary monolayers not only effectively broaden the family of 2D materials but also provide promising candidates for optoelectronic and thermoelectric materials.